Cytogenetic effects of ionizing radiation in Crepis tectorum growing within 30 km of the Chernobyl atomic power station.

Cytogenetic effects of chronic irradiation in Crepis tectorum populations growing within 30 km of the Chernobyl atomic power station were determined by scoring the frequency of chromosome aberrations in first-mitosis-metaphases of root meristematic cells during seed germination. In the first year after the accident there were large differences in the distributions of radionuclides on the plots where the three studied populations were growing. Gamma-irradiation exposure rates were in the range 5-10 mR h-1 (beta-irradiation exposure rates were about 10 times higher). The highest frequency of cells with chromosome aberrations was 9.1% in Population 1, in which cells with multiple aberrations were often observed. In the second year after the accident, six populations were studied growing in plots with exposure rates ranging from 0.02 to 20 mR h-1. Chromosome aberrations were found in 1.4 and 2.2% of the cells at the two highest exposure rates. In a few cases, seedlings were observed where all cells of the root meristem had the same chromosome aberration; in 20 cases these aberrations were heterozygous and in one it was homozygous. The highest frequencies of such karyotypic alterations in the root were 6.2 and 6.6% at the two highest exposure rates. Reciprocal translocations, inversions and complex rearrangements with increased or decreased amounts of genetic material were registered among such changed karyotypes. The presence of plants with altered karyotypes may indicate the existence of active microevolutionary processes in chronically irradiated populations.